This invention relates to an absorption refrigerator of natural circulation type employing water as a refrigerant and an aqueous solution of lithium salt as an absorbing medium. More particularly, this invention relates to an absorption refrigerator of natural circulation type in which low-temperature energy is utilized as a heat source for the generator.
U.S. Pat. No. 2,282,503 discloses a prototype of absorption refrigerators of natural circulation type with which the present invention is concerned. The refrigerator disclosed in the U.S. patent above cited employs water as a refrigerant and a lithium salt or salts such as lithium chloride or lithium bromide as an absorbing medium, and these salts are present in the form of an aqueous solution thereof in the refrigeration system.
In the absorption refrigerator of natural circulation type above referred to, the aqueous solution of the lithium salt is heated to boil in a generator and is lifted through a gas-liquid lift into a separator located at an upper level according to the principle of an air lift pump, and is separated into water vapor and the residual concentrated lithium salt solution in the separator. This water vapor is subsequently cooled to condense in a condensor, and the condensate or water is fed to an evaporator. The water fed to the evaporator is vaporized again since the internal pressure of the evaporator is sufficiently low to such an extent that the water can be readily vaporized. Due to the fact that vaporization of the water takes heat and thus produces cooling energy, another fluid flowing through the evaporator is cooled and this cooled fluid is suitably utilized as a source of refrigeration, for example, for cooling of rooms.
In the meantime, the concentrated lithium salt solution separated from the water vapor in the separator is supplied to a heat exchanger to be subject to heat exchange with a dilute lithium salt solution described later, and the concentrated lithium salt solution thus cooled down to a low temperature is then fed to an absorber. In the absorber, this concentrated lithium salt solution absorbs the water vapor produced in the evaporator to turn into a dilute lithium salt solution. This dilute lithium salt solution is subsequently fed to the heat exchanger to be subject to heat exchange with the concentrated lithium salt solution as above described, and the dilute lithium salt solution thus heated as a result of the heat exchange is returned to the generator again. The cycle above described is repeated to carry out the desired refrigeration.
However, when the temperature of the heating medium or hot water supplied to the generator is reduced to a value lower than a lower limit, boiling of the dilute lithium salt solution would not occur in the generator. It is therefore impossible to operate the prior art refrigerator of this kind in the desired manner. Further, even when the temperature of the heating medium or hot water is conversely increased beyond a predetermined setting, the concentration of the lithium salt solution is not increased although the amount of the circulating refrigerant is increased. Thus, the rate of absorption of the refrigerant in the concentrated lithium salt solution in the absorber is not increased, and a part of the refrigerant of increased amount cannot be vaporized in the evaporator to provide an unavailable refrigerant which does not contribute to the refrigeration.
U.S. Pat. No. 3,177,930 discloses an improved absorption refrigerator of this kind in an attempt to overcome the defect pointed out above. In this improved absorption refrigerator, a vessel forming substantially a U-tube is provided between the separator and the evaporator so that the concentration of the lithium salt solution can be varied by varying the amount of the refrigerant stored in the reservoir. While fairly satisfactory results could be obtained with such absorption refrigerator, it has been difficult to properly control the amount of the refrigerant stored in the refrigerant reservoir due to a great pressure variation in the evaporator.
It is therefore a primary object of the present invention to provide improvements in the structure and arrangement of the absorption refrigerator disclosed in said U.S. Pat. No. 3,177,930. In the improved absorption refrigerator of natural circulation type according to the present invention, the refrigerant reservoir is closed at one end thereof and a cooling water conduit extends into the refrigerant reservoir for maintaining substantially constant the temperature of the refrigerant stored in the refrigerant reservoir, so that the vapor pressure in the refrigerant reservoir can be maintained substantially constant and the amount of the refrigerant stored in the refrigerant reservoir can thereby be controlled depending on the difference between the pressure in the separator and that in the refrigerant reservoir.
In accordance with one aspect of the present invention, there is provided an absorption refrigerator of natural circulation type employing water as a refrigerant and lithium salt as an absorbing medium, comprising a generator for heating to boil a dilute lithium salt solution, a separator for separating water vapor expelled in said generator from the concentrated lithium salt solution, a condenser for condensing the water vapor separated in said separator, an evaporator for revaporizing the water or refrigerant condensed in said condenser by heat exchange with another fluid, an absorber for reintroducing the water vapor generated in said evaporator into said separated concentrated lithium salt solution thereby diluting said concentrated lithium salt solution, and a U-tube disposed in the conduit portion between said condenser and said evaporator, said U-tube being connected at one end thereof to said conduit portion and at the other end thereof to a refrigerant reservoir, wherein the improvement comprises a cooling conduit extending into said refrigerant reservoir for maintaining substantially constant the internal pressure of said refrigerant reservoir so as to control the amount of the refrigerant stored in said refrigerant reservoir depending on the pressure differential across said U-tube, whereby the concentration of said lithium salt solution circulating through the refrigeration system can be controlled depending on the temperature of the heating medium supplied to said generator so as to compensate for variations of the refrigerating capacity due to variations of the heating temperature.
In accordance with another aspect of the present invention, there is provided an absorption refrigerator of natural circulation type employing water as a refrigerant and lithium salt as an absorbing medium, comprising a generator for heating to boil a dilute lithium salt solution, a separator for separating water vapor expelled in said generator from the concentrated lithium salt solution, a condenser for condensing the water vapor separated in said separator, an evaporator for vaporizing the water or refrigerant condensed in said condenser by heat exchange with another fluid, an absorber for reintroducing the water vapor generated in said evaporator into said separated concentrated lithium salt solution thereby diluting said concentrated lithium salt solution, and a U-tube disposed in the conduit portion between said condenser and said evaporator, said U-tube being connected at one end thereof to said conduit portion and to said separator to receive the pressure in said separator and at the other end thereof to a refrigerant reservoir, wherein the improvement comprises a cooling conduit extending into said refrigerant reservoir for maintaining substantially constant the internal pressure of said refrigerant reservoir so as to control the amount of the refrigerant stored in said refrigerant reservoir depending on the difference between the pressure in the U-tube portion connected to said separator and that in the U-tube portion connected to said refrigerant reservoir, whereby the concentration of said lithium salt solution circulating through the refrigeration system can be controlled depending on the temperature of the heating medium supplied to said generator so as to compensate for variations of the refrigerating capacity due to variations of the heating temperature.